Walkers and Tyrrells both make the same basic thing - crisps - but in very different ways. Walkers is the biggest crisp-maker in the country. Tyrrells is tiny by comparison. But success for both depend on how their crisps are made - on what happens inside the factory. Raw materials: Crisp-making at Tyrrells starts with its raw materials - the potatoes grown in fields near its factory. Tyrrells make much of their crisps being hand-made but they're keen users of information technology. "Magic eyes" - electronic sensors - are dotted throughout the factory and monitor and control all aspects of the production process. Different types of production: Walkers' manufacturing is continuous flow - continually producing as many crisps as possible as cheaply as possible. Tyrrells, on the other hand, operate batch production - in other words constantly making short runs of products. Crisp-making means meeting crucial standards in areas like quality, hygiene and food safety, and the environment. Tyrrells scores environmentally - it's a prime example of local production. But aren't they bad for you? Health worries have hit crisp sales in recent years. Walkers' answer? Make healthier crisps, promoted in a campaign starring Gary Lineker. But how do Tyrrells' crisps compare in health terms? And regardless of the brand, are we just eating too many salty snacks?